In the confectionery industry, it is known to produce products that comprise an internal core and one or more layers of coating of the core itself obtained with different products. In particular, there exists in the confectionery industry the need to coat particularly frail cores, such as for example those that form the internal part of the products Rocher® or Raffaello® produced by the present applicant, which are generally constituted by two half-shells of wafers set facing one another and filled with cream. The coating of the shells is normally constituted by a first layer of chocolate and by a second layer of sugary syrup. Both of the layers are obtained by spraying and subsequent solidification or evaporation of the materials sprayed. To render the coating possible it is necessary for the cores that are to be coated and/or the intermediate products that are being coating to be kept in rotation in such a way that, during the movement of rotation and revolution, a desired amount of coating product will be deposited and uniformly distributed over the outer surface of each individual core or intermediate product. Coating with sugary syrups requires that each operation of spraying of sugary syrup will be followed by a step of rest and then a step of drying and/or desiccation. Desiccation is performed by directing onto the intermediate product, partially or completely coated, a flow of air that, when removed, carries along with it the moisture of the sugary syrup, causing it to evaporate. The operations described above, repeated a number of times, enable formation on the cores of coatings of different thicknesses.
For the operations of coating described above, it is known to use single coating machines operating on batches, said machines being known by the term “rotary coating pans”, which entail, however, long machine down times for loading/unloading and washing, or else coating machines operating continuously, for example of the type described in the U.S. patent application No. US2007/0275163A1. Said machines comprise a motor-driven hollow drum, which can rotate in a direction of rotation about a longitudinal axis of its own and houses a motor-driven body wound in a helix or spiral, coupled in a fluid-tight way to the inner surface of the drum. During coating, the drum is rotated whilst the spiral body is kept fixed within the drum for a pre-set period for delimiting, together with the drum, a succession of chambers for treatment of the cores.
The spiral body is, instead, rotated with respect to the hollow drum and independently of the hollow drum itself by a dedicated electric motor of its own to displace the cores axially towards an outlet of the drum and in succession between one chamber and the adjacent one.
In known machines of the type described above, in at least part of the chambers, a delivery nozzle is provided for spraying the material used for coating the cores, and a blower head for delivering a drying air flow for drying the sprayed coating material.
Known machines of the type described above, albeit used, are far from satisfactory from a functional standpoint above all for the reason that the combination of the rotation of the drum in a pre-set direction of rotation and of the independent rotation of the spiral body determines, during the coating process, a high degree of rubbing of the cores against one another and against the internal surfaces of the drum and of the spiral body, with the consequence that, even after relatively short periods of treatment, there is a progressive abrasion of the cores themselves with the undesirable formation of crumbs and powder. The formation of crumbs and powder is then all the more accentuated, the more friable and delicate are the cores.
In addition, in known machines of the type described above, as a result of the rotation in a single direction of the drum, the mass of cores contained in each of the chambers sets itself in a position inclined with respect to a horizontal plane and remains in said position for the entire duration of the treatment of the cores present in the chamber itself. The inclined arrangement of the mass of cores imposes arrangement of the delivery nozzle and of the blower head within the chamber itself, in a given position, in order for said equipment not to be buried in, or interfere with, the mass itself. The positions so far envisaged, within the drum, for the delivery nozzle and for the blower head, are not, however, yet functionally optimal. In fact, the current relative positioning, which is conditioned by the shortage of space available inside the coating drum, means that, during coating, part of the coating syrup sprayed by the delivery nozzle, inevitably hits the blower head, dirtying it to the point of modifying the distribution and direction of the flow of air delivered, with the result that the drying is no longer homogeneous.
Furthermore, once again during coating, part of the flow of air fed by the blower head intersects the jet of coating syrup, perturbing it and consequently rendering adjustment and setting-up of the spraying system problematical.
Finally, in known machines it is not possible or at least it is extremely problematical to vary the thermodynamic conditions within each of the chambers arbitrarily, and this prevents execution of a number of drying steps; i.e., it prevents variation of the characteristics of the air as the characteristics of the coating materials vary.
Finally, known machines are relatively complex from the constructional standpoint, require strict machining tolerances and high structural undeformability, it being necessary always to ensure the tightness between the outer casing and the spiral body whatever the size of the product to be treated, while cleaning thereof is extremely laborious and, in any case, subordinate to removal of the helical body from inside the drum, which involves anything but negligible difficulties.